OBJECTIVE: Our purpose was to develop a specific polymerase chain reaction detection method for 16 micro-organisms in amniotic fluid and to correlate its performance with bacterial cultures and preterm delivery occurrence. STUDY DESIGN: The study group was made up of 50 patients with preterm labor and intact membranes. The control group consisted of 23 patients not in labor and undergoing amniocentesis for either karyotype or lung maturity studies. Polymerase chain reaction and bacterial cultures were assayed in amniotic fluid of all patients. Results were correlated with pregnancy outcome. RESULTS: Polymerase chain reaction identified micro- organisms in 23 cases in the study group (46%), whereas cultures identified only 6 (12%). All control samples were negative for polymerase chain reaction and cultures. The sensitivity of polymerase chain reaction and cultures for the identification of patients delivering before 34 weeks' gestation was 64% and 18%, respectively. CONCLUSION: A polymerase chain reaction gene amplification method was developed to identify 16 microorganisms in amniotic fluid. Compared with bacterial cultures, polymerase chain reaction amplification in amniotic fluid appears to be more sensitive in identifying patients delivering prematurely.